[PATCH] DaVinci SPI: Fix SPI clock prescale factor computation

[PATCH] DaVinci SPI: Fix SPI clock prescale factor computation

[thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ]

[PATCH] DaVinci SPI: Fix SPI clock prescale factor computation

------------------------------------------------------------------------------

[PATCH] DaVinci SPI: Fix SPI clock prescale factor computation

[thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ]

From: Thomas Koeller <thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ@public.gmane.org>

Computation of the clock prescaler value returned bogus results if
the requested SPI clock was impossible to set. It now sets either
the maximum or minimum clock frequency, as appropriate.

Signed-off-by: Thomas Koeller <thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ@public.gmane.org>
---
 drivers/spi/davinci_spi.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/davinci_spi.c b/drivers/spi/davinci_spi.c
index 956f617..02e1a76 100644
--- a/drivers/spi/davinci_spi.c
+++ b/drivers/spi/davinci_spi.c
@@ -153,7 +153,7 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
 	struct davinci_spi *davinci_spi;
 	struct davinci_spi_platform_data *pdata;
 	u8 bits_per_word = 0;
-	u32 hz = 0, prescale;
+	u32 hz = 0, prescale = 0, clkspeed;
 
 	davinci_spi = spi_master_get_devdata(spi->master);
 	pdata = davinci_spi->pdata;
@@ -190,10 +190,16 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
 	set_fmt_bits(davinci_spi->base, bits_per_word & 0x1f,
 			spi->chip_select);
 
-	prescale = ((clk_get_rate(davinci_spi->clk) / hz) - 1) & 0xff;
+	clkspeed = clk_get_rate(davinci_spi->clk);
+	if (hz > clkspeed / 2)
+		prescale = 1 << 8;
+	if (hz < clkspeed / 256)
+		prescale = 255 << 8;
+	if (!prescale)
+		prescale = ((clkspeed / hz - 1) << 8) & 0x0000ff00;
 
 	clear_fmt_bits(davinci_spi->base, 0x0000ff00, spi->chip_select);
-	set_fmt_bits(davinci_spi->base, prescale << 8, spi->chip_select);
+	set_fmt_bits(davinci_spi->base, prescale, spi->chip_select);
 
 	return 0;
 }
-- 
1.7.0.3


------------------------------------------------------------------------------

Re: [PATCH] DaVinci SPI: Fix SPI clock prescale factor computation

[Grant Likely]

On Mon, Apr 26, 2010 at 3:01 AM,  <thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ@public.gmane.org> wrote:
> From: Thomas Koeller <thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ@public.gmane.org>
>
> Computation of the clock prescaler value returned bogus results if
> the requested SPI clock was impossible to set. It now sets either
> the maximum or minimum clock frequency, as appropriate.
>
> Signed-off-by: Thomas Koeller <thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ@public.gmane.org>
> ---
>  drivers/spi/davinci_spi.c |   12 +++++++++---
>  1 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/spi/davinci_spi.c b/drivers/spi/davinci_spi.c
> index 956f617..02e1a76 100644
> --- a/drivers/spi/davinci_spi.c
> +++ b/drivers/spi/davinci_spi.c
> @@ -153,7 +153,7 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
>        struct davinci_spi *davinci_spi;
>        struct davinci_spi_platform_data *pdata;
>        u8 bits_per_word = 0;
> -       u32 hz = 0, prescale;
> +       u32 hz = 0, prescale = 0, clkspeed;
>
>        davinci_spi = spi_master_get_devdata(spi->master);
>        pdata = davinci_spi->pdata;
> @@ -190,10 +190,16 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
>        set_fmt_bits(davinci_spi->base, bits_per_word & 0x1f,
>                        spi->chip_select);
>
> -       prescale = ((clk_get_rate(davinci_spi->clk) / hz) - 1) & 0xff;
> +       clkspeed = clk_get_rate(davinci_spi->clk);
> +       if (hz > clkspeed / 2)
> +               prescale = 1 << 8;
> +       if (hz < clkspeed / 256)
> +               prescale = 255 << 8;
> +       if (!prescale)
> +               prescale = ((clkspeed / hz - 1) << 8) & 0x0000ff00;

Is be appropriate to WARN_ON() or WARN_ONCE() when the clamp condition
occurs?  Particularly the condition where the minimum clock speed is
higher that the requested clock.

I'd also consider an if / else if / else structure for readability and clarity.

g.

------------------------------------------------------------------------------

[PATCH] DaVinci SPI: Fix SPI clock prescale factor computation

[thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ]

From: Thomas Koeller <thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ@public.gmane.org>

Computation of the clock prescaler value returned bogus results if
the requested SPI clock was impossible to set. It now sets either
the maximum or minimum clock frequency, as appropriate.

Signed-off-by: Thomas Koeller <thomas.koeller-x9WYMywdo8BF6kxbq+BtvQ@public.gmane.org>
---
 drivers/spi/davinci_spi.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/davinci_spi.c b/drivers/spi/davinci_spi.c
index 956f617..5c69d78 100644
--- a/drivers/spi/davinci_spi.c
+++ b/drivers/spi/davinci_spi.c
@@ -153,7 +153,7 @@ static int davinci_spi_setup_transfer(struct spi_device 
*spi,
 	struct davinci_spi *davinci_spi;
 	struct davinci_spi_platform_data *pdata;
 	u8 bits_per_word = 0;
-	u32 hz = 0, prescale;
+	u32 hz = 0, prescale, clkspeed;
 
 	davinci_spi = spi_master_get_devdata(spi->master);
 	pdata = davinci_spi->pdata;
@@ -190,10 +190,16 @@ static int davinci_spi_setup_transfer(struct spi_device 
*spi,
 	set_fmt_bits(davinci_spi->base, bits_per_word & 0x1f,
 			spi->chip_select);
 
-	prescale = ((clk_get_rate(davinci_spi->clk) / hz) - 1) & 0xff;
+	clkspeed = clk_get_rate(davinci_spi->clk);
+	if (WARN_ON(hz > clkspeed / 2))
+		prescale = 1 << 8;
+	else if (WARN_ON(hz < clkspeed / 256))
+		prescale = 255 << 8;
+	else
+		prescale = ((clkspeed / hz - 1) << 8) & 0x0000ff00;
 
 	clear_fmt_bits(davinci_spi->base, 0x0000ff00, spi->chip_select);
-	set_fmt_bits(davinci_spi->base, prescale << 8, spi->chip_select);
+	set_fmt_bits(davinci_spi->base, prescale, spi->chip_select);
 
 	return 0;
 }
-- 
1.7.0.3


------------------------------------------------------------------------------